MIT International Journal of Electrical and Instrumentation Engineering, Vol. 2, No. 2, Aug. 2012, pp. (88-93)
ISSN 2230-7656 (c) MIT Publications
88
A Research Review of Power Quality
Problems in Electrical Power System
Anurag Agarwal
Electrical & Electronics and
Instrumentation Department
MIT, Moradabad (UP), INDIA
Sanjiv Kumar
Delhi Technological University
Delhi, INDIA
Email: activesanjiv007@rediffmail.com
Sajid Ali
Electrical Department
MIT, Meerut (UP), INDIA
Email: sajidali.ali01@gmail.com
ABSTRACT
Power quality issues have become important to electricity consumers at all levels of usage. Sensitive equipment and
non-linear loads are now more commonplace in both the industrial commercial sectors and the domestic environment.
The dominant application of electronics today is to process information. The computer industry is the biggest user of
semiconductor devices, and consumer electronics. Due to the successful development of semiconductors, electronic system
and controls have gained wide acceptance in power, information and computing technology and due to the continuous
use of drive systems (rotating machines, controlling thyristor and associated electronic components) in industry and in
power stations, and the need to keep such systems running reliably, electronic equipment are becoming an integral part
of today’s industrial, institutional, and commercial facilities. Unfortunately, the same type of equipment often generates
power supply disturbances, which in turns affect other items of equipment, and are more likely to generate the distorting
harmonics. These harmonics can cause power to be used inefficiently and can be a source of premature equipment failure
that will halt production in industrial processing, will result in loss of life in hospitals, data processing activities in real
time such as banking transaction processing may be lost, etc. The principal aim of this paper is to investigate the most
common power quality problems, the effect of the harmonics on the power quality, the ways of evaluating the amount of
harmonic distortion present in a power system which lead to isolate the cause of the problem and finally device a solution
for a good power quality.
Keywords: Power quality, monitoring equipments, mitigation techniques.
I.
INTRODUCTION
Power quality problem in the power system has gained
importance since the late 1980s. The interest in Power Quality
(PQ) is related to all three parties concerned with the power
i.e. utility companies, equipment manufacturers and electric
power consumers. Problems affecting the electricity supply
that were once considered tolerable by the electric utilities
and users are now often taken as a problem to the users of
everyday equipment. Understanding power quality can be
confusing at best. There have been numerous articles and
books concerning power quality[10]. There are two terms
known in power systems about the quality of power: Good
power quality and poor power quality. Good power quality can
be used to describe a power supply that is always available,
always within the voltage and frequency tolerances and has
a pure noise-free sinusoidal wave shape to all equipment,
because most equipment was designed on that basis[13].
Unfortunately, most of the equipment that is manufactured also
distorts the voltage[12] on the distribution system, leading to
what is known as poor power quality. And thus affecting other
equipment that was designed with the expectation of consistent
undistorted voltage, and are thus sensitive[11] to power
disturbances resulting in reduced performance and will cause
equipment miss operation or premature failure. The cost of
power quality problems can be very high and include the cost
of downtimes, loss of customer confidence and, in some cases,
equipment damage. Indeed, power quality is an important
point in the relationship between suppliers and consumers[12]
but might become a contractual obligation that stress on
improving voltage quality, availability, performance[8] and
efficiency and these improvements will have: Benefits for
industrial customers (customized and flexible availability)
and for suppliers utilities.
II.
CLASSIFICATION AND IMPACT OF
PQ PROBLEMS
To make the study of Power Quality problems useful,
the various types of disturbances need to be classified by
magnitude and duration.
MIT International Journal of Electrical and Instrumentation Engineering, Vol. 2, No. 2, Aug. 2012, pp. (88-93)
ISSN 2230-7656 (c) MIT Publications
2.1
Undervoltages
Short duration under-voltages are called “Voltage Sags” or
“Voltage Dips [IEC]”. Voltage sag[17, 18] is a reduction in
the supply voltage magnitude followed by a voltage recovery
after a short period of time. Excessive network loading, loss
of generation, incorrectly set transformer taps and voltage
regulator malfunctions, causes under voltage. Loads with a
poor power factor or a general lack of reactive power support
on a network also contribute. Under voltage can also indirectly
lead to overloading problems as equipment takes an increased
current to maintain power output (e.g. motor loads).
2.2 Voltage Dips
89
electrical environments, which cause owners, industrial
companies and investors a great deal of frustration and
disappointment and in many cases, result in a great loss of time
and money, and that lead us to ask a valuable question “What
is the problem?” The answer to this question could have one
or more of the following points:
– Computer malfunctions
– Interrupted manufacturing sequences
– Catastrophic failures
– Erratic equipment behaviour
– High electrical maintenance cost.
But whatever the answer is, Chapman [7] has classified
them as a power quality problems and the latter is subdivided
into two categories:
• Supply system quality problems.
• Installation and load related problems.
The major cause of voltage dips on a supply system is a fault
on the system, i.e. sufficiently remote electrically that a voltage
interruption does not occur. Other sources are the starting of
large loads and, occasionally, the supply of large inductive
loads [18]. The impact on consumers may range from the
annoying (non-periodic light flicker) to the serious (tripping 3.2 Supply System Quality Problems
of sensitive loads and stalling of motors).
• Supply interruption
• Transient interruption
2.3 Voltage Surges/Spikes
• Transients
Voltage surges/spikes are the opposite of dips – a rise that • Undervoltage/over voltage
may be nearly instantaneous (spike) or takes place over a
• Voltage dip/voltage surge
longer duration (surge). These are most often caused by
lightning strikes and arcing during switching operations on • Voltage imbalance
circuit breakers/contactors (fault clearance, circuit switching, • Flicker
• Harmonic distortion
especially switch off of inductive loads).
According to Douglas et al. [6] the above problems can
be classified into one of three disturbance categories based
III. FREQUENCY VARIATIONS
upon duration: Transient disturbances include unipolar
Frequency variations that are large enough to cause problems Transients, oscillatory transients (such as Capacitor switching),
are most often encountered in small isolated networks, due localized milliseconds. Transients can originate internally
to faulty or maladjusted governors. Other causes are serious within the building or externally on utility power lines. They
overloads on a network, or governor failures, though on an represent about 12 to 15% of all power line problems. These
interconnected network, a single governor failure will not Disturbances can cause:
cause widespread disturbances of this nature.
• Damage to electronic lighting systems
• Shutdown to sensitive equipment
• Immediate or latent damage to digital
• Microprocessor controlled equipment.
Monetary disturbances are voltages increases or decreases
(sags, swells, and interruptions) lasting more than 10
milliseconds but less than three seconds. The majority
of voltage sags result on utility lines from faults on the
Distribution or transmission lines and they represent about 60%
of all power problems. Voltage swells are the least frequent
of the Power line problems representing about 2 to 3% of all
Figure 1: Different Problems encountered with PQ
power problems occurring to industry studies [10].
These momentary disturbances can cause:
3.1 Causes of Power Quality Problems
• Sudden decrease in line loads
In today’s fast-paced environments, a huge amount of money
is spent on sate of the art computer controlled equipment and • loosing wiring
systems. These systems are often installed in “unfriendly” • Re-energizing of power after a utility power
MIT International Journal of Electrical and Instrumentation Engineering, Vol. 2, No. 2, Aug. 2012, pp. (88-93)
ISSN 2230-7656 (c) MIT Publications
Interruption, when power comes back in. Steady-state
disturbances are voltage increases or decreases (under voltages,
over voltages, and interruptions). Interruptions and power
outages can originate from electrical short circuits in Building
wiring or on utility power lines. These interruptions will cause
electrical, computer and electronic equipments shut down and
losses in operations and revenues.
90
earth Leakage currents will seek alternative routes to earth.
This may result in current flowing in unexpected places with
consequent risk should the system be disconnected.
3.3.3
Voltage Dips, Flat Topping and Transients
Heavy loads such as air conditioning systems, large motors
during the starting process, principally cause Dips. However,
3.3 Installation and Load Related Problems flat topping is caused by electronic equipment such as the
start -up of printers. The combination of surges and dips in
The major problems in this category can be classified [5] in the voltage lead to what is known as voltage Flicker and this
one of the three following groups:
latter is caused by the operation of large cyclic loads and can
• Harmonic currents
reduce the life of motors drives and electrical contacts.
• Earth (Ground) leakage currents
• Voltage dips and transients
3.3.1
Harmonic Currents
These currents will cause wiring, motors and transformers
to overheat. The result may be a breakdown of insulation
and a significant reduction of equipment lifespan. Some of
the adverse effects of concentrated nonlinear loads upon a
facility are:
- Nuisance tripping of circuit breakers
- Overvoltage problems
- Metering problems
- Overheating of transformers and induction motors’
- Computer malfunctions
- Metering problems
- High levels of neutral-to-ground voltage
- Power factor rate penalties
All non-linear loads generate harmonics. This includes all
loads, which use switching to control or convert power, for
example:
- Switched mode power supplies— computers, office
equipment, domestic equipment:
- Variable speed motor drives
- Thyristor controlled heating elements
- Dimmer switches
- Solid state fluorescent la mp ballasts
- Over loading magnetic devices such as motors, lamp ballast
and transformers as a result of saturation of the magnetic
core material.
3.3.2
Earth Leakage Currents
The principal design consideration for an earthling system
is that it must protect people and animals from receiving
potentially fatal electric shocks in the event of a fault condition.
Now, earth conductors are carrying large leakage current
permanently as well as serving as a sink for high frequency
noise currents. If for any reason the connection to earth is poor,
then the impedance of the primary earth route will be high and
IV. OBJECTIVE OF A POWER QUALITY
SURVEY
The power quality survey is the first, and perhaps most
important, step in identifying and solving power problems
cited previously. In other words it is thus designed to locate,
identify and eliminate the electrical disturbances which
disrupt data collection networks, PLCs, variable speed
motor drives thyristor controlled heating elements and other
sensitive electronic equipment that contain some 162 form of
microchip or “logic circuits”. There are two types of power
quality surveys: The first type is a preventative survey, uses a
Number of tests and inspections to locate potential Problems
before they cause a production outage. The second type is,
a troubleshooting survey, it is used to locate and eliminate
problems as quickly as possible after a production outage.
Whether the investigation involves a simple piece of equipment
or the facility’s entire electrical system, the survey process
typically requires the following steps [6].
• Planning and preparing the survey
• Inspecting the site
• Monitoring the power
• Analysing the monitoring and inspection data
• Applying corrective solutions.
From the above steps, the survey should provide the
background information and basic methodology and tools
required to benchmark the power quality performance and
improve the reliability with respect to interruptions. Thus,
the process basically involves finding out the What, Where,
When, How and Why of the power related Problems at hand.
Monitor requirements[3,4]: what are the requirements or
what are the specific equipment resources needed, to get the
job done. Where to monitor: depends on where the Problems
are observed or suspected. When to monitor: The time when
the problem occurs can also provide important clues about
the nature of the power problem. If the problem occurs at a
certain time of day, the equipment switched on at that time
should be suspect. The monitoring period should last at least
as long as one “business Cycle,” which is how long it takes
for the process in the facility to repeat itself.
MIT International Journal of Electrical and Instrumentation Engineering, Vol. 2, No. 2, Aug. 2012, pp. (88-93)
ISSN 2230-7656 (c) MIT Publications
–
–
–
–
–
How long to monitor.
Data collection and analysis systems.
Indices for describing performance.
Results of other benchmarking efforts from around the world.
Other benefits of the bench marking effort. As part of the
planning and preparation process it is necessary to obtain a
site history for the facility of equipment being investigated.
Asking questions of equipment operators or others familiar
with operations is an important part of a site history.
4.1
Inspecting the Site
The site examination begins by visually inspecting outside the
facility and around the immediate vicinity in order to gains
a better perspective of the utility service area. Inspecting
the facility helps to identify equipment that might cause
interference. It will also surface electrical distribution system
problems such as broken or corroded conduits, hot or noisy
transformers, poorly fitted electrical panel covers and more.
Any inspection should include a physical review of the wiring
from the critical load to the electrical service entrance and any
loads, which might cause power problems, will be identified.
4.2
Monitoring the Power
To solve a power problem for a single unit of equipment, the
monitor should be placed as close to the load as possible.
Looking for a power quality problem, need that voltage
signal is monitored and finally to find the cause, accurate
measurement of power quality issues requires that the monitor
accurately [4] measure the voltage and current waveforms.
4.3
Analyzing the Monitoring and Inspection
Data
To identify equipment problems, it is key to analyse data
in a systematic manner. First, look for power events that
occurred during intervals of equipment malfunction. Second,
identify power events that exceed performance parameters
for the affected equipment. Third, review power monitor
data to identify unusual or severe events. Finally, correlate
problems found during the Physical inspection with equipment
symptoms.
V.
SOLUTIONS
5.1
Solutions to Supply System Quality
Problems
91
has a different problem solving function and can be used
in a variety of applications. Voltage regulators are installed
between the power source and sensitive equipment to control
the incoming voltage in order to sustain a constant output
voltage, it protects the equipment against overvoltage’s and
under voltages. However, Transient Voltage Surge Suppressors
(TVSS) cuts noise and voltage transients only, and it does not
regulate voltage to limit surges and sags.
5.2
Solution of Harmonic Problems
With current technology, virtually all of today’s high
performance electronic equipment uses static power rectifiers,
which convert alternating current to direct current, and the
reverse. It pulls a non-linear current and the latter induces
voltage distortion and when 163 distorted voltage is delivered
to equipment designed to expect a sinusoidal voltage, the
result is overheating or malfunctions. Harmonic currents are
a fact of life and cannot be eliminated unless nonlinear loads
are avoided, all industry is increasingly exposed. Although
future developments may provide improved electronic systems
producing lower levels of harmonics, the problem must be
addressed in current and future installations. Since harmonic
currents cannot be prevented, installations must be designed
to cope with them. Utility companies impose limits on the
Harmonic voltage distortion, which a customer’s site can
impose on the system. Where the utility limits are exceeded,
special additional steps must be taken to filter the harmonic
content. Active harmonic filters] are now becoming available
which inject an exactly complimentary harmonic current
into the supply to cancel that produced by the non-linear
loads. Harmonic filters will provide a solution, although all
ramifications of their use may not be anticipated in advance.
Filters types include line-reactors, passive harmonic filters,
active harmonic filters, electronic feedback filters and special
transformers that use out of phase windings to accomplish
harmonic reduction] While these units are effective at reducing
the harmonic current as seen by the utility, they do not reduce
the harmonic current flowing in the cables of the installation.
According to Martin[5] practicing the following measures
minimizes the effect of harmonics: Take account of harmonic
generating loads when planning the installation.
• Reduce the number of socket outlets on each circuit and
increase the number of circuits.
• Carefully distribute these circuits among the phases to reduce
out of balance currents.
• Increase the cross sectional area (CSA) of feeders.
• Two sizes up is a good rule of thumb with a sound technical
justification— and it saves energy too!
The potential solutions for such problems are dependent on
the type of disturbance. However, for the voltage disturbances, • Increase the CSA of neutral feeders and distribution panels
- twice the phase CSA is recommended. The old practice of
such as momentary outage, sags and swells and transient
using half sized neutrals is definitely no longer satisfactory!
voltages, the most convenient solutions to improve the
performance of a sensitive equipment is to install a protective • Uses 5 core copper cable—one core for each phase and
device between the power source and sensitive equipment.
two for the neutral. Keep circuits, which supply harmonic
There is a wide variety of protective devices [1,2], each device
generators- such as office equipment and variable speed
MIT International Journal of Electrical and Instrumentation Engineering, Vol. 2, No. 2, Aug. 2012, pp. (88-93)
ISSN 2230-7656 (c) MIT Publications
•
•
•
•
•
drives separate from those supplying harmonic hating Loads
such as induction motors:
Maintain records of cable layout and usage.
Maintain and upgrade the system carefully.
Consult the relevant records before making changes.
Routinely monitor neutral and phase currents.
Check for excessive heating in transformers, motors and
distribution boards.
92
these devices is supplied to the system through an inverter on
a momentary basis by a fast acting electronic switch. Enough
energy is fed to the system to replace the energy that would
be lost by the voltage sag or interruption.
6.3
Filters
Initially, lossless passive filters (LC) have been used to reduce
harmonics, and capacitors have been chosen for power-factor
correction of nonlinear loads. Active filters (AFs) [24, 25]
have been explored in shunt and series configurations to
5.3 Solution of Earth Leakage Problems
compensate for different types of non-linear loads. These are
The primary purpose of grounding electrical systems is to shunt-connected devices used to eliminate harmonics. Either
protect personnel and property if a fault (short circuit) were to passive (LC or RLC) networks or active (voltage source
occur. The second purpose of a grounding system is to provide converter) technologies are possible.
a controlled, low impedance path for lightning induced currents
to flow to the earth harmlessly. Problems can be avoided if it is 6.4 Static Var Compensators (SVCS)
recognized that the grounding system in electrical installations This is a shunt-connected assembly of capacitors, and possibly
is no longer designed solely for fault conditions. Wherever reactors, which provides reactive power to a network during
modern electronic equipment is used, the earth acts as a key disturbances to minimize them. It is normally applied to
working component of the electrical installation. As such, it transmission networks to counter voltage dips/surges during
must be given equal consideration in terms of:
faults and enhance power transmission capacity on long
transmission circuits.
– Impedances
– Connections
– Documentation
– Working practices
VI. MITIGATION EQUIPMENTS
Mitigation equipment exists for each of the above
power-quality problems. Some of this equipment are listed
below:
6.1
Thyristor-Based Static Switch
The static switch is a versatile device for switching a new
element into the circuit when voltage support is needed. To
correct quickly for voltage spikes, sags, or interruptions, the
static switch can be used to switch in one of the following:
– Capacitor
– Filter
– Alternate power line
– Energy storage system.
The static switch can be used in the alternate power line
application. This scheme requires two independent power lines
from the utility. It protects against 85% of the interruptions
and voltage sags.
6.2
VII. CONCLUSIONS
The present paper gives an assessment of power quality. Various
issues concerning PQ have been highlighted and discussed. The
paper also discusses about various issues related to power
quality classification and characterization of disturbances,
propagation of disturbances, and measurement strategies
being used to monitor the power quality.Semiconductors
are the heart of computer industry; unfortunately these
electronic components are non-linear and thus may affect the
safe or reliable operation of computers and computer-based
equipment. Often more important than the physical effect
on the equipment is the loss of productivity resulting from
computer equipment failure, miscalculations and downtime.
And thus changes in the equipment on site will change the
harmonic Profile, so rendering the filters ineffective. Thus
due to the technology and software now available, monitoring
is highly-effective means to detect, solve, and even prevent
problems on both utility and customer, it can detect problem
conditions throughout the system before they cause equipment
malfunctions, and even equipment damage or failure. However,
before monitoring a design step is needed and should take into
account the electrical environment and define how the electrical
installation must meet the needs of the business.
Energy Storage Systems
Storage systems can be used to protect sensitive production [1]
equipment from shutdowns caused by voltage sags or
momentary interruptions. These are usually dc storage systems,
such as UPS, batteries, superconducting magnet energy [2]
storage (SMES) [23], storage capacitors etc. The output of
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